1. Field of the Invention
This invention relates to a method of making a chip scale package, and more specifically to a method of making a molded chip scale package with a flip-chip configuration.
2. Description of the Related Art
As electronic devices have become more smaller and thinner, the velocity and the complexity of IC chip become more and more higher. Accordingly, a need has arisen for higher package efficiency. Demand for miniaturization is the primary catalyst driving the usage of advanced packages such as chip scale packages (CSP) and flip chips. Both of them greatly reduce the amount of board real estate required when compared to the alternative ball grid array (BGA) and thin small outline package (TSOP). Typically, a CSP is 20 percent larger than the chip itself. The most obvious advantage of CSP is the size of the package; that is, the package is slightly larger than the chip. Another advantage of CSP is that the package facilitates test and burn-in before assembly as an alternative to known good die (KGD) testing. In addition, CSP can combine many of the benefits of surface mount technology (SMT), such as standardization, encapsulation, surface mount, and reworkability, with the benefits of flip chip technology, such as low inductance, high I/O count, and direct thermal path.
However, CSP has at least one disadvantage compared to conventional BGA and TSOP, namely, high cost per unit. However, this problem could be eliminated if chip-sized packages could be mass produced more easily. Therefore, there is a need in the semiconductor packaging industry for CSP using mass production techniques at the wafer-level, as is illustrated in U.S. Pat. No. 5,323,051, U.S. Pat. No. 5,925,936 and U.S. Pat. No. 6,004,867.
Disclosed in the technical article by Baba et al. titled, xe2x80x9cMolded Chip Scale Package for High Pin Count,xe2x80x9d Proceedings of the 46th ECTC, Orlando, Fla., 1996, pp. 1251-1257, is a process for making a CSP 100 (see FIG. 4) which is shown in greater detail in FIG. 5. As shown in FIG. 1, the IC chip 10 has a plurality of rerouted under bump metallurgy (UBM) 12 electrically connected to bonding pads on its active surface. First, copper lands 22 and inner solder bumps 24 are formed on a base frame 20 made of ferroalloy. The copper lands 22 are formed by plating and the inner solder bumps 24 are formed onto the copper lands 22 by stencil printing. Then, the chip 10 is attached onto the inner solder bumps 24 of the base frame 20, using flip chip bonding technology. Second, as shown in FIG. 2, the bonded chip 10 and portions of the frame 20 are encapsulated with a package body 30 by a molding process identical to that used in conventional molding of IC packages. Third, as shown in FIG. 3, the base frame 20 is separated from the encapsulated chip 10 in a way that transfers the copper lands 22 and the inner solder bumps 24 from the base frame 20 to the chip 10. Finally, as shown in FIG. 4, solder balls 40 are attached to the exposed surfaces of the transferred copper lands 22.
FIG. 5 shows in greater detail the chip 10 with an external solder ball 40. The chip 10 has a bonding pad 12 formed on its active surface. The bonding pad 12 and the external solder ball 40 are connected through wiring conductor pattern 50, UBM 12, inner solder bump 24 and transferred copper land 22. The package body 30 is capable of providing stress relief in the solder joints due to CTE mismatch between chip and substrate. The CSP shown in FIG. 4 has advantages of compact package size, good electrical performance, and high reliability. However, as can be appreciated from the above prior art processes, the method of making CSP 100 is rather complex and costly.
It is therefore an object of the present invention to overcome, or at least reduce the problems and disadvantages associated with the above-described technique for fabricating a molded chip scale package.
It is a further objective of the present invention to provide a simplified method which can be used to produce a molded chip scale package.
The method of making a chip scale package in accordance with the present invention comprising the following steps: (a) providing a semiconductor chip having a plurality of metal bumps formed on the active surface thereof; (b) providing a metal plate having a plurality of flip-chip pads formed on a surface thereof; (c) positioning the semiconductor chip on the surface of the metal plate with the metal bumps on the chip aligned with the flip-chip pads on the metal plate; (d) connecting the metal bumps on the active surface of the semiconductor chip to the flip-chip pads on the surface of the metal plate; (e) encapsulating the semiconductor chip against a portion of the surface of the metal plate; (f) removing the metal plate while leaving the flip-chip pads intact; and (g) forming a plurality of solder balls on the flip-chip pads.
Using the technique of the present invention, it becomes possible that the manufacture of a molded chip scale package can be relatively simplified and economical, yet highly reliable.